FIG. 1 is a block diagram illustrating a mobile unit such as a vehicle or vessel with a conventional mobile satellite tracking antenna mounted.
As shown in FIG. 1, conventional mobile satellite tracking antennas 111 and 121 are generally mounted on a mobile unit, for example, a vehicle 110 and a vessel 120. Although the vehicle 110 and the vessel 120 joggle due to mechanical vibration or external impact, the conventional mobile satellite tracking antennas 111 and 121 stably direct a target satellite 101 to receive or to transmit satellite broadcasting.
The mobile satellite tracking antennas 111 and 121 include a sensor unit and a mechanical driving unit. The sensor unit senses the motion of the mobile unit such as the vehicle or the vessel, and the mechanical driving unit drives a satellite antenna to direct a target satellite using sensor signals measured at the sensor unit. In order to accurately drive the satellite antenna to direct the target satellite 101 in spite of the motion of the mobile unit 110 or 120, the information contained in the sensor signal is very important. Also, a motor controlling unit that drives the driving unit according to the information of the sensor signal also performs important functions.
As a sensor technology for a conventional mobile satellite tracking antenna, an electric noise removing technology, an inclination angle sensor technology, and an angular velocity sensor technology were introduced. Hereinafter, the shortcomings of the conventional sensor technologies will be described,
Among the conventional sensor technologies, the electric noise removing technology removes the electric noises from sensor signals by passing an inclination angle sensor signal and an angular velocity sensor signal through a low frequency passing filter in a sensor unit.
However, it is very difficult to correct the error of an inclination angle against the motion angle of a mobile unit due to external vibration and impact. In case of the angular velocity sensor signal, a temperature drift phenomenon occurs due to temperature variation that is general characteristic of an angular velocity sensor unit. It is also very difficult to correct the error of the angular velocity sensor signal generated by the temperature drift.
As another conventional technology, a technology for controlling a posture of a satellite tracking antenna was introduced. In this conventional technology, the posture and the location of the satellite antenna are controlled by feeding back an inclination angle only. Or, the speed is controlled by feeding back an angular velocity sensor only. In case of controlling the location and the posture only, the control performance is deteriorated by the error of the inclination angle sensor. Or, in case of controlling the speed only, the control performance is deteriorated by the temperature drift.
In a conventional technology for controlling a posture of a satellite antenna, the posture of the satellite antenna mounted at a mobile unit such as a vessel is controlled by feeding back inclination angular velocity and inclination angular acceleration, thereby improving the responsibility thereof. In the conventional technology, an inclination angle and a first inclination angular velocity are sensed. Also, a second inclination angel velocity is sensed at a base unit. Then, a driver motor is controlled using a PID controller based on the sensor signals. The PID controller controls the driving motor that drives a pedestal by comparing a predetermined target value with the inclination angle and the second inclination angle velocity. That is, the conventional technology for controlling a posture of a satellite antenna was introduced to secure responsibility and predictive to sustain the optimal antennal receiving sensitivity although the mobile unit joggles.
However, these conventional technologies have shortcomings of using a low frequency pass filter for processing sensor signals and have various difficulties to compensate the errors of the sensor signals caused by external impact or vibration.